The field of this invention relates to a thermostatically controlled mixing valve and more particularly to a thermostatic controlled mixing valve with a volume control feature incorporated therein.
Mixing valves are well known and common in the plumbing field. These valves provide a flow of mixed water from separate hot and cold water supplies. Secondly, thermostatic control for handle mixer valves are well known. One reason for thermostatic control is to eliminate constant readjustment of the valve when the temperature of the hot water supply fluctuates. The temperature of the hot water supply may vary substantially. Furthermore, the pressure within the cold water line may also vary changing the proportions of hot and cold water flow and thereby fluctuating the temperature of the mixed water.
Known thermostatic valves have packaging problems and are often significantly bulkier than standard mixing valves that do not incorporate the thermostatic regulation. This bulkiness is due to the flow path that has always been used for thermostatic faucets, namely the supply inlets approach the centrally located thermostatic valve from a radially outer position.
When thermostatic valves are incorporated into mixer valves, the volume or flow control valves may be installed either downstream or upstream from the thermostatic valve element. When the flow is regulated downstream of the thermostatic element within the mixed water flow, installation of non-return valves are needed in order to prevent the possibility of communication between the hot water supply and the cold water supply. When the flow control of the hot and cold water supplies is upstream of the thermostatic valve before the water is mixed, the return valves are not needed. For this economic reason, most thermostatic mixing valves have the volume control upstream of the thermostatic element.
However when the flow is regulated with respect to the hot and cold water supplies, the thermostatic device is unable to maintain the constant temperature due to the variations of the flow rates. It is well known that when hot and cold water supply pressures are approximately equal or with the hot supply pressure being only slightly lower than the cold water pressure, the difference in flow rate or variation between the hot and cold water supplies is increased when the total flow is reduced and the rise in temperature can sometimes become significant. On the other hand, if the hot water supply pressure is substantially lower than the cold water supply pressure, as is often the case due the increased corrosion of the hot water pipelines, the difference in the flow rate or variation of the flow rate between the hot and cold water supplies is decreased as the total flow rate is reduced.
Contoured apertures in a pair of disc plate valves have been known to contour the water flow profile between the hot and cold water supplies. However, these plate valves are set to move both rotatably and translationally with respect to each other to mechanically control both the total flow rate and the temperature mix of the hot and cold water.
A thermostatic mixing valve has been developed that includes two inlets for hot water and cold water, a mixing chamber, passages between the inlets and the mixing chamber, an outlet for the mixed water which runs from the mixing chamber, an expanding thermostatic element placed, at least in part, within the outlet so that it will be in contact with the mixed water. A slide valve is activated by the thermostatic element and acts on one or both of the inlet passages to maintain the mixed water at a constant temperature. The inlets are located in a central body situated inside the slide valve activated by the thermostatic element. A pair of valve plates crossed by passages for the water are positioned to control total flow rate through the inlets for the hot water and cold water without affecting the outlet for the mixed water. The valve plates are controlled by rotation of an external body or housing of the thermostatic mixing valve. A thermostatic mixing valve of this kind has proved to be very advantageous, yet (like other types of thermostatic mixing valve) it can prove to be inconvenient in certain conditions.
If a thermostatic mixing valve, which is designed to be able to deliver a determined rate of flow, supplies a device downstream which, due to its own high resistance only allows delivery of a much lower rate of flow, the fall in pressure at the inlet produced by the pair of valve plates is greatly reduced in comparison to the fall in pressure at the inlet produced by the downstream device and the pressure inside the thermostatic mixing valve is close to the pressure in the supply pipes. If a considerable difference in pressure then occurs between the hot and cold water supplies, for example because of the actuation of a device with high rate of flow that uses primarily hot or cold water upstream from thermostatic valve, the valve will then be unstable and will start to oscillate, because of the cross-flow which occurs inside the thermostatic valve. The oscillation will cause malfunctioning and temperature instability in the mixed water delivery downstream from the thermostatic valve. This situation may occur when a thermostatic mixing valve is designed to supply a relatively high rate of flow, such as for example 50 or 60 liters per minute at 3 bars but is used with a much lower delivery rate, for example 9 liters per minute due to the resistance or restriction at the outlet on certain downstream devices. This situation occurs, for example, when the thermostatic mixing valve is installed to supply a bank with multiple outlets, each of which is equipped with its own on/off valve, and the user makes use of only one outlet. More generally, the situation occurs when the thermostatic mixing valve is capable of supplying many devices and only one or a few of these devices are actually in operation at any given time.
In fact, the user could in theory prevent this instability by accurate regulation of the thermostatic mixing valve, so as create a resistance at the inlet that proportional to the resistance at the outlet. However, this is not possible in practice, because well-known thermostatic mixing valves do not offer sufficiently sensitive regulation at low rates of flow. Furthermore, since the rate of flow is limited at the outlet of a device with high restriction or resistance, the user is not aware of the effect of the regulation at the downstream device and is therefore not in a position to decide whether the regulation he has carried out is adequate to avoid the noted problem.
This problem which also occurs with other kinds of thermostatic mixers, has usually been remedied by installing a pressure controller in the supply pipes upstream of the thermostatic mixing valve. This pressure controller, however, increases the size, complexity and expense of the installation and renders the device less reliable.
What is needed is a compact thermostatic valve that is easily assembled and controls the temperature of the mixed water output. What is also needed is a thermostatic control built into a valve with flow control that provides proper thermostatic control at a wide range of flow rates.
In accordance with an aspect of the invention, a thermostatic mixing valve has a cold water inlet port and a hot water inlet port in communication with a base having two supply ports. A handle body is rotatably mounted onto the base and is operably connected to a first valving surface with two inlet passages therethrough that are operably positioned adjacent the two supply ports for controlling total flow rate into the housing. A thermostat element is operably connected to a second valving surface to move the second valving surface between a first and second seat for controlling the relative flow from the first and second inlet passages in response to the temperature of fluid in the mixing chamber.
The ports and the first valving surface are incorporated in two concentrically mounted plates that can be rotated with respect to each other and provided with openings therethrough for the controlled passage of the fluid through the two plates. The opening in one of the valve plates which control the inlet pipes for hot water or cold water is constructed so as to sub-divide the whole field of regulation determined by the relative rotation of the plates into at least two successive fields. The first field of regulation is positioned adjacent to the shut off position is and formed by a narrow section of the opening. The second field of regulation is positioned and after the first is formed by a wide section of the opening. The first and second fields are preferably inserted into both the hot water and cold water passages.
When the thermostatic mixing valve has to supply one or more devices, which provide a low flow rate, it is positioned into its first field of regulation, which occurs as soon as the thermostatic mixing valve is moved from its closed position. The narrow section of at least one of the inlet passage openings then causes a relatively marked fall in pressure, even in the presence of a low flow rate caused by high resistance at the outlet, and renders the thermostatic mixing valve practically and advantageously stable to even significant differences in pressure between the supply pipes. When the thermostatic mixing valve is used to supply devices with large flow rates, the thermostatic valve is positioned to its second field of regulation. The wide section of the inlet opening enables delivery of large flow rates. Under the condition, any differences in pressure between the hot and cold supply, even if significant, do not cause temperature fluctuation problems.
It is desirable to provide an intermediate field of regulation interposed between the two fields of regulation determined by the narrow and large sections in the openings respectively. The intermediate section has a width which is intermediate between those of the other two fields of regulation.
It is also possible to use inlet passage apertures for both valve plates which have special shapes. Preferably, one of the valve plates (for example the fixed one) should have inlet openings which have the conventional shape of an elongated curved slot. The other valve plate (for example the moveable one) should have inlet openings shaped with different passage sections to determine the two or more distinct fields of regulation of the thermostatic mixing valve.
In one embodiment of the invention, the inlet openings of one of the valve plates are in the shape of elongated slots. At least one of these has a first section of reduced width, a second section of enlarged width and, optionally, an intermediate section of width which is intermediate between the widths of the first and second sections. In another embodiment of the invention, the inlet opening of one of the valve plates has large, uniform width. At least one of these openings has only a first section that extends fully through the plate. A second section has a limited depth and does not fully pass through the valve plate. An optional intermediate section of greater depth than that of the second section can be provided between the first section and the second section.
In another embodiment of the invention the openings include sections that fully passes through the plate and at least one section of limited depth that does not fully pass through the valve plate which has a narrower width and is adjacent a narrow slot section.
In accordance with another aspect of the invention, visible indicators on parts of the thermostatic mixing valves inform the user which field of regulation the thermostatic mixing valve is operating in at any given time. In addition or alternatively for the visible indicators, devices with an elastic or detest release, can give the user a tactile warning of passage of the thermostatic mixing valve from one to another field of regulation. This device is useful in making it very easy for the user to identify the field of regulation of the thermostatic mixing valve which is most suitable.
In this fashion, a compact thermostatic cartridge is provided. The cartridge can be housed in a mixer valve flow regulator with volume or flow rate control disc plates that have contoured apertures to assure set flow ratios between the hot and cold water supplies independent of the total flow rate through the disc plates.